Dear Jim, Open 60 Class Rules require there to be 5 watertight bulkheads across the boat, thus making 6 compartments. Also, and this seems to be a very good idea, there is a requirement that there exist, in physical buoyance within the construction of the boat, 130% of the displacement. In other words, if the hull is intact, you can fill it up with water, and it will still float, even with the keel on. For Great American III for Vendée Globe 2008 I recall that Thierry Dubois, who built the boat, had made the deck especially thick with its core material, 40 millimeters, and that was where he put the extra required buoyancy.
Question submitted by Jim, Floral Park, NY, USA